Various types of wireless communication networks, which have been in practical use nowadays such as customer-owned systems, for example, wireless LAN, Bluetooth, and the like and public network systems, for example, mobile phone, PHS, and the like function independently of each other at present, and users selectingly use them according to applications, areas, communication speeds, and the like.
Since these wireless communication networks have various communications speeds, service areas, communication costs, and the like depending on the types thereof, it is necessary to appropriately switch the networks depending on a location where they are connected in place of using a particular network at all times.
At the time, it is required a seamless handover technology that integratingly handles the respective systems, selects an appropriate network and switches a network being used to it without causing a user to be aware of the switching, and executes communication continuously without interrupting it.
As the method described above, it is contemplated to separate a network, through which communication is executed to control switching of network and the like, from a network through which data communication is executed. It is known a method of establishing data communications and audio communication also in a wireless communications system that does not have a paging function originally by using a wide area wireless communications system as disclosed in, for example, PCT application (PCT/JP02/13187) proposed by the applicants.
According to the technology, it is proposed to use a wide area wireless communications system having a paging function of, for example, a pager line and the like as an exclusive as well as to use, for example, wireless LAN and the like as the wireless communications system and to utilize them by combining the characteristics of them, respectively.
The method intends to effectively utilize existing infrastructures, in particular, the pager line and the like. However, since a whole system is constructed by previously determining a particular network as a control network, a problem arises in that the system does not function in locations, for example, an oversea area, an isolated island, and the like where the control network cannot be used.
Further, even when a plurality of networks can be used for data communication, the data communication cannot be executed while continuously switching the networks. In particular, when communication is switched between wireless communication networks to which base stations are connected at positions different in network, a technology for not only switching a terminal wireless system promptly but also properly switching a data transmission path on a network side is necessary, and it is desired to realize the technology.
Further, in the network making use of the wireless communication terminal, the wireless communication terminal does not start to switch the network until it moves out of an area providing the network service. Accordingly, the network is disconnected once and must be connected again to a service being provided, from which a problem arises in that continuity of connection cannot be secured.